The tone-scaling processes used to render a digital medical image for output (hardcopy or softcopy) can often result in the loss of definition of the skin-line. Knowledge of the location (and associated gray levels) of the skin-line would allow the tone-scale process to be done in a manner that preserves the definition of the skin-line. Segmentation of the body part from the background (area of direct exposure) and foreground (unexposed area behind masking) can be problematic at the skin boundary due to the gray levels overlapping those of the foreground which limits the effectiveness of thresholding techniques. On the other hand, techniques that utilize spatial information (e.g., texture measures) have inherent limitations at boundaries due to the finite spatial window of pixels over which the measures are computed. Knowledge of the skin-line may allow improved segmentation or body part detection. Additionally, the shape of the skin-line boundary may be an effective feature for identifying the body part or exam type (e.g., chest vs. hand). It is therefore desirable to provide a method for the detection of the skin-line in digital medical imaging.
U.S. Pat. No. 5,452,367, issued Sep. 19, 1995, inventors Bick et al., discloses a method of skin-line detection including the step of first segmenting the body part from the foreground and background. The segmentation is based on the proximity of a pixel's gray level value to the peak of the global histogram, the gray level range over a 7.times.7 local window of pixels, and the membership of the pixel to a large connected region. After segmentation, the contour distinguishing the segments is inspected and processed to define the skin-line. This method is disadvantageous in requiring segmentation before skin-line detection.